Solenoid pump

ABSTRACT

A method of reducing or eliminating vibration in a linear reciprocating solenoid pump  10,  the method comprising the steps of providing a solenoid pump  10  having a linear reciprocating plunger  14  and providing an electric circuit  48  to energize electro-motion means  16  of the solenoid pump  10,  the electric circuit  48  energizing the electro-motion means  16  with an increased frequency of n times the frequency of normal mains electricity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 200710100946.5 filed in China on 28 Apr. 2007.

BACKGROUND OF THE INVENTION

This invention relates to solenoid pumps and more particularly to reducing or eliminating vibration and/or noise caused during operation.

Solenoid pumps are well known, and typically comprise a pump housing and a linear reciprocating plunger slidable therein to pump liquid between an inlet and an outlet.

However, vibration caused by the unbalanced movement of the mass of the plunger, and consequently noise associated therewith, is undesirable and can result in premature fatigue, wear and failure of the pump.

The present invention seeks to overcome or mitigate this problem.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method of reducing or eliminating vibration in a linear reciprocating solenoid pump, the method comprising the steps of:

-   -   providing a solenoid pump having a linear reciprocating plunger;         and     -   providing an electric circuit to energize electro-motion means         of the solenoid pump, the electric circuit energizing the         electro-motion means with an increased frequency of n times         normal mains electricity frequency.

Preferably, n is chosen to avoid operating the pump at its natural resonance frequency.

Preferably, n is a whole number greater than 1.

Preferably, the electric circuit includes a full bridge rectifier and a MOSFET to provide the increased frequency.

Alternatively, the electric circuit includes a bidirectional thyristor connected in series with the electro-motion means.

According to a second aspect of the invention, there is provided a solenoid pump comprising: a pump housing having a liquid inlet, a liquid outlet, and a plunger chamber; a plunger received for linear reciprocating movement in the plunger chamber; electro-motion means for electromagnetically moving the plunger; and an electric circuit for energizing the electro-motion means with a frequency n times greater than normal mains electricity frequency, where n is a number greater than

Preferably, the plunger is hollow and includes a plunger head which is slidably received in the plunger chamber and an elongate plunger rod which is slidably received in a pump chamber.

Preferably, the electric circuit includes a full bridge rectifier and a MOSFET for providing the increased frequency.

Alternatively, the electric circuit includes a bidirectional thyristor in series with a coil of the electro-motion means.

Preferably, the increased frequency is different to the natural resonance frequency of the pump.

Preferably, n is a whole number greater than 1.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a cross-sectional plan view of one embodiment of a solenoid pump, in accordance with the second aspect of the invention;

FIG. 2 shows a first electric circuit used to energize the solenoid pump;

FIG. 3 illustrates time graphs of various parts of the circuit of FIG. 2;

FIG. 4 shows a second electric circuit used to energize the solenoid pump; and

FIG. 5 illustrates time graphs of various parts of the circuit of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1 of the drawings, there is shown a solenoid pump 10 which comprises a pump housing 12, a linear reciprocatable plunger 14, and electro-motion means 16 for moving the plunger 14 in a reciprocating manner. The electro-motion means is preferably, in the form of a solenoid.

The pump housing 12 includes a hollow housing body 18 having two open ends 20 and a stepped-bore 22 therethrough. A plunger chamber 24 is provided within the housing body 18 and is defined primarily by the stepped-bore 22. A first one of the open ends 20 of the housing body 18 forms a liquid inlet port 26 for liquid flow into the plunger chamber 24, and an end cap 28 is fastened, typically by bolts, to the housing body 18 to close a second one of the open ends 20.

The end cap 28 includes a central rectilinear liquid-outlet passage 30 therethrough. The liquid-outlet passage defines a pump chamber 32 leading from the plunger chamber 24. The plunger chamber 24 is cylindrical and the pump chamber 32 is coaxially aligned with the cylinder axis of the plunger chamber 24. The liquid outlet port 26 is shown as also being coaxially aligned.

The plunger 14 is hollow and comprises a plunger head 34 and an elongate hollow plunger rod 36 rigidly fixed to the plunger head 34. The plunger head 34 includes a recess 35 with an opening in a base of the recess. The plunger rod 36 includes an axially extending uniform through-bore 37, with one end being received in the opening in the base of the recess 15. A lateral cross-section of the through-bore of the plunger rod 36 is smaller than a lateral cross-section of the recess of the plunger head 34. In this way, a stepped through-bore through the plunger 14 is formed by the recess of the plunger head 34 and the through-bore of the plunger rod 36. The plunger head 34 is a sliding fit within the plunger chamber 24. Holes 41 are provided to equalize fluid pressure within the plunger chamber on either side of the plunger head.

A coiled return spring 38 is included within the plunger chamber 24. The return spring 38 extends from the plunger head 34 to contact the first open end 20 adjacent to the liquid inlet port 26. A step in the stepped base 22, provides a seal for the return spring 38. The return spring 38 biases the plunger head 34 towards the pump chamber 32.

A coiled buffer spring 40 is also included within the plunger chamber 24, interposed between the plunger head 34 and the end cap 28. The plunger rod 36 extends coaxially within the buffer spring 40. The in use buffer spring 40 prevents the plunger head 34 from contacting the associated end cap 28. A plate or disc 54 provides a seat for the buffer spring 40. Disc 54 may be of a rubber based material to further dampen vibrations from the plunger 14 and buffer spring 40 being transferred to the end cap and housing.

The plunger rod 36 is dimensioned to be a clearance sliding fit within the pump chamber 32. A seal 33, preferably in the form of a rubber O-ring, seals the plunger rod 36 to the pump chamber 32 while allowing the plunger rod to slide with respect to the pump chamber 32 along the plunger axis. The seal 33 is held on a step in the pump chamber 32 by a seal retainer 43. In this way, the seal 33 also acts as a plunger guide, stabilising the plunger 14 during use.

The plunger rod 36 thus has an open end disposed within the pump chamber 32. The open end is closed by a non-return valve 56 formed by a seal body 58 which is pressed against the open end of the plunger rod by a valve spring 60. The non-return valve 56 allows fluid to enter the pump chamber 32 through the hollow plunger rod 36 but cannot exit the pump chamber via the plunger rod.

A restriction in the bore of the pump chamber 32 forms an outlet port which is fitted with a non-return valve 62 having a spring 60 and a seal body 58, which is pressed against the outlet port to prevent liquid entering the pump chamber 32 through the outlet port. Spring 60 is held in the outlet passage 30 by a retaining tube pressed into the outlet passage 30.

In operation, sliding movement of the plunger rod causes fluid to be pumped through the pump chamber. As the plunge rod is withdrawn partially from the pump chamber, liquid enters the pump chamber through the plunger rod to fill up the space left by the withdrawing plunger rod. When the plunger rod is moved in the opposite direction, to be inserted further into the pump chamber, the displaced liquid is expelled through the outlet port with the non-return valve preventing liquid movement in the opposite direction.

The electro-motion means 16 includes an electromagnetic stator 42 comprised of an annular electromagnet 44 supported by and surrounding the housing body 18 of the solenoid pump 10 on an exterior surface thereof, an armature 46 comprised of the plunger head 34 and formed of an electromagnetic material, and an electric circuit 48 for energizing the electromagnetic stator 42.

In use, the electromagnet 44 is energized with electrical current in a pulsating manner. This current, when flowing through the coil of the electromagnet, causes a magnetic field to be generated which, due to the electromagnetic stator, causes the plunger to be drawn to the right (as shown in FIG. 1) against the urgings of the return spring 38 to align the plunger head, functioning as the armature, into the gap 45 formed in the magnetic path of the stator. When the current through the coil is turned off, the armature is released and the plunger is moved to the left (as shown in FIG. 1) under the resilient urgings of the return spring and as buffered by the buffer spring 40. Movement of the plunger head causes movement of the plunger rod as discussed above to pump liquid through the pump chamber.

Traditionally, the coil is connected to mains supply via a diode providing a half wave rectified waveform giving a simple pulse for each cycle of the mains power, thus also providing a half cycle rest period for the return spring to pump the liquid out of the pump chamber.

The present invention modifies the input wave form so as to increase the number of pulses per cycle of mains frequency while still giving sufficient rest time between pulses for the return spring to move the plunger when the electromagnet relaxes so as to do useful work. Vibration is reduced by having a lower stroke length of the plunger but pump volume (capacity) is not sacrificed due to the higher pumping frequency.

Although many complex circuits are available for modifying voltage waveforms and changing the frequency of mains power, two simple circuits will be discussed which each provide a doubling of the operating frequency of the solenoid pump.

FIG. 2 illustrates a first preferred circuit 48. Mains power is connected across a full wave bridge rectifier 50 to generate the typical rectified waveform of FIG. 3( a). The output of the bridge rectifier 50 is applied to a series connected circuit of the solenoid 10 and a MOSFET 51. A flywheel diode 72 and resistor 73 are placed across the solenoid. A voltage divider resistor network, resistors 70, 71 are connected across the bridge output to provide a reduced voltage to the Gate terminal of the MOSFET 51. Thus, when the voltage of the divider circuit is higher than the open voltage of the Gate terminal, the MOSFET turns ON and the solenoid is energized. Otherwise, the MOSFET is OFF and the solenoid id de-energized. The ON/OFF time of the MOSFET is shown in FIG. 3( b) and the solenoid current wave form is shown in FIG. 3( c) where the decay current through the flywheel diode is noted.

The ON/OFF time of the MOSFET can be adjusted by changing the values of the divider resisters 70, 71. Thus, the pump operates at 2 times the inputted mains power frequency.

The circuit of FIG. 4 illustrates another preferred circuit 48 a. AC mains frequency power is applied across a series circuit of the solenoid coil 10 and a bidirectional thyristor 52. The input voltage waveform is shown in FIG. 5( a). Two resistors 74, 75 and a capacitor 76 are arranged to form a delay trigger circuit to the Gate terminal of the thyristor. When the voltage across the thyristor is close to the maximum value, the thyristor is turned ON and the solenoid is energized. The thyristor once triggered stays on until the current through it becomes zero (as occurs when the voltage changes polarity). The ON/OFF time of the thyristor 52 is shown in FIG. 5( b) and the current through the solenoid is shown in FIG. 5( c). The solenoid is, of course, de-energized when the thyristor 52 turns OFF.

Once the solenoid is energized, whether by positive or negative current, it will induce a magnetic field attracting the plunger, thus compressing the return spring. During the OFF time, the spring relaxes pushing the plunger into the pump chamber to pump the liquid. Thus again, the pump operates at twice mains frequency.

Although the drive circuits can be, in theory, applied to a standard solenoid pump, in practice, the plunger and springs are configured to operate at a desired frequency and the mass of the plunger is chosen to have a natural resonance frequency greater than the operating frequency but not significantly greater to give the plunger a certain momentum during operation. By simply changing the operating frequency, there is a possibility that the pump will not work or will go into natural resonance and generate uncontrolled vibrations.

As resonance frequency is proportional to the square root of the reciprocal of mass, it may be desirable, as a rough calculation, to reduce the mass of the plunger by a factor of n √1/m where n=the number of times the mains frequency is increased, i.e. f_(o)=nf_(m) where f_(o)=operating frequency, f_(m)=mains frequency, n=integer, so as to maintain the natural frequency higher than the operating frequency.

However, as most pump designs are not so finely tuned, for a doubling of input frequency, a halving of plunger mass and plunger stroke length will produce a pump with similar output and significantly reduced vibrations making this design a good solution for improving solenoid pump designs.

The plunger stroke length can be modified by changing the spring force and the electro-magnetic power of the solenoid.

It has been determined that, when vibration occurs in a normal standard solenoid pump 10 having a single linear reciprocating plunger 14, the vibration and thus generated noise can be eliminated, or at the very least significantly reduced, by reducing the mass of the plunger 14 by 1/n times, by then reducing the amplitude of movement of the plunger 14 by 1/n times, and finally by increasing the frequency of the electricity applied to the electromagnetic stator 42 to n times normal mains frequency.

This inter-relationship provides for markedly reduced, or elimination of, vibration and consequently noise.

The mass of the plunger can be easily altered by standard manufacturing or workshop techniques, for example by altering the material of manufacture or by removing material via machining.

Although the mass of the plunger and its operating amplitude are reduced, the pumping rate is not significantly impacted. Consequently, the reduced or eliminated vibration, resulting in improved reliability and longevity, is preferred.

Although n has been suggested above as being 2, n can be any number which is greater than 1. Also, preferably, n is a whole number. Ideally, n can be chosen to avoid the natural resonance frequency of the pump.

An actual optimum value of n for a particular series of solenoid pumps can be derived by monitoring the pump, and then making appropriate changes to the mass of the plunger and the associated energizing circuitry. As such, it may be found that, for a particular series of pumps, n may be 3 or even 4.

It will also be appreciated that any circuit means can be provided for energizing the electromagnetic stator of the electro-motion means, providing the amplitude of the plunger and the frequency of the electrical energization can be controlled and set.

The embodiments described above are given by way of example only, and various other modifications will be apparent to persons skilled in the art without departing from the scope of the invention, as defined by the appended claims. 

1. A method of reducing or eliminating vibration in a linear reciprocating solenoid pump, the method comprising the steps of: providing a solenoid pump having a linear reciprocating plunger; and providing an electric circuit to energize electro-motion means of the solenoid pump, the electric circuit energizing the electro-motion means with an increased frequency of n times normal mains electricity frequency.
 2. The method of claim 1, wherein n is a whole number greater than
 1. 3. The method of claim 1, wherein the electric circuit includes a full bridge rectifier and a MOSFET to provide the increased frequency.
 4. The method of claim 1 comprising providing the electric circuit with a bidirectional thyristor connected in series with the electro-motion means.
 5. The method of claim 1, further comprising selecting n to avoid operating the pump at its natural resonance frequency.
 6. A solenoid pump comprising: a pump housing having a liquid inlet, a liquid outlet, and a plunger chamber; a plunger received for linear reciprocating movement in the plunger chamber; electro-motion means for electromagnetically moving the plunger; and an electric circuit for energizing the electro-motion means with a frequency n times greater than normal mains electricity frequency, where n is a number greater than
 1. 7. The solenoid pump of claim 6, wherein the plunger is hollow and includes a plunger head which is slidably received in the plunger chamber and an elongate plunger rod which is slidably received in a pump chamber.
 8. The solenoid pump of claim 6, wherein the electric circuit includes a full bridge rectifier and a MOSFET for providing the increased frequency.
 9. The solenoid pump of claim 6, wherein the electric circuit includes a bidirectional thyristor in series with a coil of the electro-motion means.
 10. The solenoid pump of claim 6, wherein n is a whole number greater than
 1. 11. The solenoid pump of claim 10, wherein the increased frequency is different to the natural resonance frequency of the pump. 